Error handling in Rust

Errors are managed by the type:

enum Result<T, E> {
    Ok(T),
    Err(E),
}

We can use the operator match to manage them or other ways explained below.

Unrecoverable Errors

panic!("crash and burn");

Ex. access an out of bound index in an array.

Fast retrive of value

To retrive value from a Result we can use the following methods:

.unwrap()
.expected("error message")

if Result contains an Err the program panics

Propagation

To propagate an error you can either return an Err or use the ? operator:

File::open("hello.txt")?.read_to_string(&mut s)?;

If there is an error it returns the error otherwise it gets the value requested.

Validation

If we need to validate a certain value we can create a custom type and use the constructor as validator:

pub struct Guess {
    value: i32,
}

impl Guess {
    pub fn new(value: i32) -> Guess {
        if value < 1 || value > 100 {
            panic!("Guess value must be between 1 and 100, got {}.", value);
        }

        Guess { value }
    }

    pub fn value(&self) -> i32 {
        self.value
    }
}

Source

https://doc.rust-lang.org/stable/book/ch09-00-error-handling.html